The developer of an apartment building that collapsed when a powerful earthquake struck southern Taiwan last week remains in custody as the likelihood of finding any survivors amid the rubble decreases.

Lin Ming-hui, the former chairman of the real estate development company that built the 17-story Weigun Golden Dragon complex in Tainan, has been charged with professional negligence resulting in death, along with two other former executives. Questions about the methods and materials used in constructing the building have emerged in the wake of the tragedy, fueled by photos from the wreckage showing tin cans and foam built into the walls of the complex.

The complex was the only major building to collapse in last Saturday's 6.4 magnitude quake, although dozens of buildings in Tainan were either destroyed or seriously damaged.

At least 43 people are believed to have been killed in the disaster. More than 300 people have been rescued from the wreckage of the apartment building, with more than 100 still missing and believed to be trapped in the debris. Rescuers continue to work around the clock in their search for survivors, using heavy machinery, electronic listening devices and their bare hands to dig through the rubble.

Officials remain optimistic of finding more survivors, despite the expiration of the 72-hour window experts give for anyone trapped underneath rubble to survive without food or drink.

Quake-prone Taiwan is in a highly active seismic zone known as the "Pacific Ring of Fire," and more than 50 fault lines pass through the island.

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U.S. State Department spokesman John Kirby told reporters Monday the U.S. Agency for International Development will make a grant of $500,000 to the Taiwan Red Cross that will "provide immediate assistance to households affected by the earthquake."

The quake struck two days before the Chinese Lunar New Year celebrations, the most important holiday in the Chinese calendar.

Liu Shih Chung, the deputy secretary general of Tainan's city government, told VOA Monday that hotels are offering to house the earthquake victims for free for one week.